1. Field of the Invention
The present invention relates to a sheet-stapling apparatus that staples center-fold booklet (sheets) by staple(s) and an image-forming system that uses such a sheet-stapling apparatus.
2. Description of Related Art
A technology to staple a bundle of sheets by a staple(s) has been known in the past. In order to allow the staple 501 to penetrate into a sheet 10P, it may have to shear apart of the sheet 10P by force for pushing the sheet 10P using the staple 501 as shown in FIG. 1A or to rupture a part of sheet 10P by force for pushing the sheet 10P using the staple 501 with fibers of the sheet 10P being extended as shown in FIG. 1B.
In both cases, the part of the sheet 10P sags by the staple 501 and when exceeding an allowable sagging amount thereof, the part of the sheet 10P opens. The staple 501 then penetrates into the opening of the sheet 10P. When increasing number of the sheets 10P, it is difficult for the staple 501 to penetrate into the sheets 10P because an apparent thickness of the sheets 10P is increased by the sag of the sheets 10P.
As shown in FIGS. 2A through 2C, the past clinch, namely, so-called spectacles type clinch in which legs of the staple are curled while the legs of the staple are still curved has performed to form a booklet. In this case, a clincher 50 mounts the booklet 10 in which plural sheets are bundled. Clincher 50 has a narrow cut 51 that allows the legs of the staple 501 to be curled.
A driver 52 drives the staple 501 to penetrate the legs of the staple 501 into the booklet 10 as shown in FIG. 2A. The driver 52 further drives the staple 501 to conduct the legs of the staple 501 penetrated into the booklet 10 to the narrow cut 51 of the clincher 50 as shown in FIG. 2B to bend them inwardly as shown in FIG. 2C.
A sheet-stapling apparatus that staples a center-fold booklet (sheets) by staple(s) has been proposed in the past as a sheet finisher for performing any staple processing on the sheets, and the like (see Japanese Patent Application Publication No. 2010-150002). It has been known that it is desirable to align a fold of each of the sheets with a position to be stapled by the staple with the prepared booklet being prevented from opening when the sheet-stapling apparatus forms the booklet by stapling the sheets using the staple(s).
Accordingly, a technology to perform any stapling processing on the center-folded booklet after the booklet is mounted has been known. As shown in FIG. 3A, when the driver drives the staple 501 to penetrate the legs of the staple 501 into the fold 10a of the center-folded booklet 10, an amount of work to be done by the staple 501 becomes larger than that done by the staple 501 in a case where the legs of the staple 501 penetrate into a flat part of the booklet 10 as shown in FIG. 3B because the staple 501 moves beyond the allowable sagging amount of the booklet 10. Accordingly, it is difficult for the staple 501 to penetrate into the booklet, so that any buckling of the staple may occur. Normally, as shown in FIG. 3C, by allowing the booklet 10 to sag, it may be easy for the staple 501 to penetrate into the booklet, which prevents the buckling of the staple from occurring.
By the way, as shown in FIG. 4, in order to clear up a difficulty for the staple to penetrate into the booklet, the staple processing has been performed in the past after a pushing member 600 has pushed the booklet 10 to a supporting member 601 to make flat a fold of the booklet to be stapled.